A very popular louver for fluorescent lighting fixtures and so-called "luminous ceilings" is known as a parabolic louver because the louver cells, which are open top and bottom, have walls which are parabolically curved from top to bottom. Parabolic louvers are made either with square cells or with circular cells supported in a square grid.
The parabolic louvers are popular not only because they are quite decorative, but also because they are the most efficient open louvers yet devised for distributing illumination uniformly over an area. They have been installed in many new or redecorated buildings, and may be found in lobby areas, elevator cars, and any other locations where their advantages may be desired.
Parabolic louvers have turned out to have one very serious practical drawback. The parabolic cell walls must be kept very clean of any dust or film that would interfere with their light reflective properties; and cleaning the cells has turned out to be a very slow and tedious hand operation.
The companies that manufacture and distribute parabolic louvers have tried for some time to develop a relatively rapid and simple and inexpensive way to clean the louvers, and one of the manufacturers entered into a contract with an independent research facility in an effort to solve the problem which was beginning to interfere with the marketability of parabolic louvers. Neither the manufacturers nor the independent research facility was successful in these endeavors, although the research facility was successful in developing a cleaning liquid which does a very superior job of removing dust and smoke film from louver cell walls.
The problems presented in caring for parabolic louvers are well illustrated by the cleaning instructions published by one manufacturer, which read as follows:
"Parabolic louvers, though extremely durable should be maintained with mild detergents, rinsed thoroughly with deionized warm clean water (not more than 120.degree.) and air dried. Never use abrasives or mechanical means for cleaning the specular surfaces of these louvers."